1. Field of the Invention
The present invention is in the field of electronic circuits, and, more particularly, is in the field of circuits that correct the input offset voltage of an operational amplifier.
2. Description of the Related Art
During the processing of DC voltage signals or low-frequency signals, direct-coupled operational amplifiers, particularly operational amplifiers in MOS technology, generate an error caused by the input offset voltage. From the journal "Elektronik", No. 20, Sept. 30, 1988, pages 97 to 104, a method is known whereby this offset voltage can be nulled during operation with the aid of a main amplifier and an auxiliary amplifier. During regular measurement intervals, the auxiliary amplifier is disconnected from the input signal and short-circuited at the input end. The resulting output level of the auxiliary amplifier is stored by means of an external capacitor. During a second measurement interval, the auxiliary amplifier is connected to the input signal at the input end and to a second external capacitor at the output end. The potentials stored in the two external capacitors are applied to the two auto-zero inputs of the main and auxiliary amplifiers, so that during operation, the effect of offset voltage errors on the output of the main amplifier is compensated. A more detailed explanation of the operation of this prior art circuit is given below in connection with FIGS. 1 and 2.